Indirect proof methods comparison – UGC NET Question

A correctly describes contradiction: assume the negation of what you want to prove and reach a contradiction. B is correct: proving the contrapositive is equivalent to proving the original conditional. D is correct: both are valid classical methods. C is false because contradiction proves the conclusion true (not both premises and conclusion false). E is false because contradiction proofs can be valid even when non-constructive. Therefore A, B and D only are correct.

Option A:
Option A is incomplete because it omits D, the statement confirming both methods are valid.

Option B:
Option B is incorrect because it includes C, which misstates the outcome of a contradiction proof.

Option C:
Option C is wrong because it omits A, leaving out the defining idea of contradiction.

Option D:
Option D is correct because it includes exactly the true statements and excludes C and E, which are false.